Doppler

The University of Vienna, founded in 1365 by Duke Rudolf IV of Austria, is the oldest continually operating university in the German speaking world., though it was not until 1384 that it received papal approval and full university status. Among its alumni, that include fifteen Nobel Prize winners, is Christian Andreas Doppler.

Doppler was born in Salzburg on November 29, 1803, to a family of master stonemasons. Physically frail and prone to illness his father had him educated with a view to participating in the administrative side of the business. His natural aptitude for mathematics led to his professor at the Salzburg Lyceum recommending that Doppler continue his education at K. K. Polytechnisches Insitut in Vienna, Graduating in 1825 Doppler moved to the University of Vienna where he studied higher mathematics, mechanics, and astronomy, later becoming assistant to Professor Adam Burg at the Polytechnisches Insitut, during which time he published several papers, A contribution to the Theory of Parallels, The Converging of an Infinite Series of Logarithms, Continued Roots and Their Convergence, Concerning the Probable Cause of Exciting Electricity by Contact and of the Electric Field, and, Concerning a Curious Characteristic of the Electric Field.

In 1835 Doppler moved to Prague to take up a teaching post at the Ständische Realschule and from 1836-1838 taught higher mathematics for four hours a week at the Prague Polytechnic, being formally appointed full professor in 1841. In 1842 he published the work for which he is best know, Über das farbige Licht der Doppelsterne und einiger anderer Gestirne des Himmels (On the coloured light of the binary stars and some other stars of the heavens).

Recognising that light is a wave Doppler proposed that since the pitch of a sound wave from a moving source varies for a stationary observer, the colour of a star should alter relative to its velocity in relation to Earth. Doppler further predicted that, “that this will in the not too distant future offer astronomers a welcome means to determine the movements and distances of such stars which, because of their unmeasurable distances from us and the consequent smallness of the parallactic angles, until this moment hardly presented the hope of such measurements and determinations.”

Though, given the instruments available to him and other astronomers of the time, it was impossible to measure such a change in stars Doppler theorized that sound waves from a moving source would also undergo the same apparent change in frequency. In 1845 the Dutch meteorologist, Christoph Hendrik Diederik Buys Ballot demonstrated the Doppler principle by observing the apparent change in pitch of horn players travelling in an open carriage pulled by a locomotive at forty miles per hour. Doppler carried out a similar experiment with pitch perfect trumpeters and in 1846 published a revision of his principle which took account of the motion of the observer as well as the source.

In 1847 Doppler accepted the professorship of mathematics, physics, and mechanics at The Academy of Mines and Forests in Banska Stiavnica. 1848, the Year of Revolution and the year of publication of The Communist Manifesto, saw popular uprisings throughout Europe. In Prague Prince Windisch-Grätz bombarded the city after radicals took to the streets following an attack by the army on a demonstration in Václavske náměstí (Wenceslas Square). Political unrest in Banska Stiavnice led Doppler to seek employment elsewhere and in 1849 he was appointed professor at the Vienna Polytechnic. On January 17, 1850, he became the first director of the new Institute of Physics at the University of Vienna where he examined the young Gregor Mendel for entry, refusing him a place after finding the future father of genetics mathematics unsatisfactory. Mendel was later admitted and studied physics under Doppler.

Suffering from tuberculosis Doppler left Vienna in November 1852 to convalesce in Venice. He died, aged 50, on March 17, 1853 and is buried in Venice in the Cimetero di San Michele where a plaque to his memory, erected by the physicists of Venice, stands in the colonnades.

In 1919 Edwin Hubble arrived at the Mount Wilson Observatory, California, where with the assistance of Milton L. Humason he first provided the final demonstration that the spiral nebulae were distant galaxies. Using Vesto Slipher’s measurements of spectral shift associated with galaxies combined with their own measurements Hubble and Humason discovered that not only were the spectra of distant galaxies redshifted (i.e., the wavelength of the light appears to be stretched as a result of the relation to the Earth and the observed star) but that the more distant the galaxy the greater the redshift appeared to be. In other words nearly everything in the universe is moving away from us, and the farther away the object is the faster it is moving. Doppler’s theory proposed in Über das farbige Licht der Doppelsterne had been conclusively demonstrated.